The present invention relates to a head positioning system of a magnetic head on a magnetic recording medium. In particular, it relates to such a system which reads out a servo pattern embedded in a recording medium, and seeks and locates a head quickly according to said servo pattern.
The present invention is applicable not only to a magnetic recording system, but also to an optical recording system, although the embodiments in the present text are directed to a magnetic recording system.
In an accurate head positioning for a high density recording, a thermal off-track is a serious problem, which comes from temperature gradient in a device. A data surface servo system is a promising technique for solving the thermal off-track problem. Conventionally, two kinds of data surface servo systems have been proposed, they are; a sector servo system, and a continuous servo system (a track servo system).
A sector servo system records an information servo pattern at the beginning of a data track. In other words, each of the circular tracks has both a servo information and a data portion, so that a head reads servo information and data alternately. Therefore, the sector servo system has the disadvantage that it can only provide servo information intermittently, but it can not provide continuous servo information. Therefore, it is not suitable for a high speed seek, and/or an accurate positioning.
A track servo system has two kinds of tracks, a servo track and a data track. Those tracks are read out by using the specific heads, a servo head, and a data head. As the servo pattern is continuous, the high resolving power servo signal may be obtained. However, it has the disadvantage that when a head seeks a track (or a head moves in the radial direction) in traversing the tracks, the servo pattern is not continuous. Therefore, a prior track servo system is not suitable for a high speed seek system, although it can provide accurate positioning by a continuous servo pattern.
Some other prior art systems for solving the above disadvantages include a buried servo system, an optical servo system, and/or hybrid servo system which has an auxiliary specific servo plane. A buried servo system uses a two layer recording medium for data and servo information, and a head reads out both data and servo information, therefore, the resolving power of a reproduced servo pattern is not enough for highly accurate positioning. An optical servo system, and a hybrid servo system are complicated in structure, and have the disadvantage that the production cost is high.